Pile Design and Construction Practice, Fifth edition

Depth to NAP datum (m)
Cone resistance qc (MN/m
0
+5
10 20 30
2 )
0
–5
–10
qc before dredging
–15
–20
–25
–30
–35
–40
q c after
dredging
Depth of dredging to 30 m
qc before
qc after
0 0.5 1.0
4.3.7 Tubular steel piles driven to deep penetration
into clays and sands
Resistance of piles to compressive loads 181
Calculated (Broug)
measured
Figure 4.20 Cone resistance versus depth before and after dredging sand (after Gijt and
Brassinga (4.27) ).
The research work undertaken at Imperial College, London, on the axial capacity of steel
tube piles has been referred to briefly in the preceding sections. This work was undertaken
on behalf of the UK Marine Technology Directorate. The design procedure adopted from the
research became known as the MTD method. It is understood that MTD no longer operates
but the work at Imperial College has been extended with analysis of further test data and has
been published in book form by Jardine et al. (4.30) The design procedures which have
evolved have become known as the ICP method.
The principal users of large tubular steel piles are the offshore petroleum industry and
recently these piles have found increasing use as monopile foundations for offshore wind
power generators. Before publication of details of the MTD method guidance for engineers
designing offshore piling was available in the recommendations of the American Petroleum
Institute (4.31) . Their recommendations for the shaft friction of piles in clay generally followed
the �c u relationship of Semple and Rigden (4.5) . Equation 4.16 was used for piles in sands
with Brinch Hansen factors of N q for calculating base capacity. Chow (4.32) found that the API
recommendations for piles in sand were over-conservative for short piles with L/B ratios up
to 30, and for dense sands with relative densities of 60% or more.